Metallurgical process



Patented Dec. 5,.

Q 1,937,934 METALLURGICAL rnocass' William F. zimmerli, Niagara Falls, N. Y., aasigner to E. I. du Pont de Nemours 8; Com-- pany, Incorporated, Wilmington, DeL, a cornotation of Delaware No Drawing. Application February a, 1932 Serial No. 590,789

3 Claims. (01. 75- 2) This invention relates to the treatment of alloys of copper and zinc, with or without the 10 gested at various times but this treatment has not met with commercial application for metals having a melting point which is higher than the boiling point of sodium (except where extremely small quantities are used) because the almost instantaneous vaporization of the sodium when it is immersed in such molten metal causes violent explosions. This is due to the great volume expansion when the solid. sodium is converted into vapor.

An object of this invention is to devise a means of adding sodium to brass so that effective treating amounts of sodium can be added to and be retained by the brass. My invention includes the brass thus obtained. A further chject is to produce brasses possessing a physical structure which readily responds to an even anneal during subsequent manufacturing processes; such a condition is to be found in metals comparatively free from non-metallic impurities.

3 Brass having a more regular structure with grains of relatively small average size ismost desirable especially when the metal is to be subjected to cold working operations such as stamping, drawing, etc.

I accomplish these objects by adding the sodium to the brass or the brass-forming materials as an alloy with another metal which is to form a constituent of the brass. I add a sodium alloy of a brass constituent in which the sodium is in such dilution that its vaporization takes place gradually to avoid the losses and inconvenience due to violent spattering as occurs when pure sodium is added.

In accordance with my invention the sodium may be added to the brass as an alloy of one of the constituent metals of the brass. Thus, if the straight copper-zinc-bra ss of certain specifled metal proportions is to be prepared I may add the sodium to the molten metals as an alloy with a portion of the zinc which is to form part of the alloy; or if a lead-brass is to be prepared I may prepare a copper-zinc alloy and then add the sodium to this by means of a sodium alloy with the lead which is to be added. Thus, also,

. the sodium may be added as an alloy with a brass containing a relatively large amount of sodium. I shall describe my invention particularly as employing the use of a zinc-sodium alloy but the principles observed will be applicable to alloys with other metals. In all cases some of the added sodium remains in the brass.

I have found that ,when a zinc-sodium alloy containing about 2% byv weight of sodium is added to a molten brass in comparatively large pieces and preferably by thrusting these pieces 55 beneath the surface of the melt, the sodium is gradually vaporized as the alloy fuses in the bath. This permits a more gradual intermingling of the vapors of the sodium with the body of the fused brass. The sodium thus vaporized comes in contact with substantially all the melt in the bath and. thus has an opportunity to produce the beneficial effects which I have found.

Example I Zinc will form an alloy with sodium up to about 2% by weight of sodium. 300 grams of zinc were melted under finely divided charcoal in a covered crucible of approximately 500 cc. so capacity; to this was added 10 grams (an excess over that required for the final alloy to allow for losses) of sodium while stirring by means of an iron rod immersed in the molten zinc through a hole in the crucible cover. Some 35 sodium is lost from the mixture as vapors. After thorough mixing this alloy' was cast in chilled molds.

3040 grams of copper were now melted under finely divided charcoal and into this were stirred 1275 grams of zinc, which was added in small portions while stirring the melt with a graphite rod. After the mixture had become homogeneous, 225 grams of the 2% sodium-zinc alloy were added by holding it beneath the surface of the melt with tongs. Some sodium fumes were evolved which stirred the melt; when these fumes had subsided the brass was cast in molds.

A microscopic examination of polished, etched sections of straight cast ingots of brass so treated present a marked difference in the structure from untreated brass. The untreated sample usually shows a relatively large number of elongated dendritic crystals with heavy grain boundaries. The treated brass shows a relatively large number of grains approaching the polyhedric structure and the grain boundaries are finer than the untreated samples with dendrites fewer in number.

These cast samples of brass were annealed I10 at 550 C. for 30 minutes and then subjected tocoldworkingtothe extentoia% reduction and re-annealed at 550 C. for minutes. A microscopic examination of etched, polished sections 0! the castings revealed that the sodiumtreatedbrasshadaverymuchmoreuniiorm grain size than the untreated brass, showing that the sodium-treated brass more readily responded to the anneal.

Other castings or sodium treated and -untreated brass were cold worked under a power hammer to the extent of a 20% reduction and then annealed at 450 C. for 30 minutes. Microscopic examination of sections of these castings revealed that in the untreated brass there was considerable variation in the. relative size of the grains, while in the sodium-treated brass the structure was more regular and average size oi the grains was finer.

Microscopic examination of untreated brass castings and castings which have been treated with sodium, after both have been annealed at 700-750" 0. without a previous cold working, showed that the grains of the annealed brass which had been treated with sodium were substantially larger in average grain size than the grains in the untreated brass after a similar anneal. when these annealed samples were cold worked with a power hammer to a 20% reduction and re-annealed at 550 C. for 30 minutes, the sodium treated sample showed a much more regular structure than the untreated brass.

There was some indication in the untreated samples of the production of strains in the metal, revealed by abnormal grain growth along the center of the rolled, strip. This was absent in the sodium treated samples.

Example II 300 grams of lead were melted under finely divided charcoal in a covered iron crucible;

into this was stirred 100 grams of sodium, about 20 grams at a time, while keeping the crucible covered as much as possible. The crucible and contents were cooled with vigorous stirring to about 370 C. at which point most of the alloy had solidified. The excess liquid was then poured off, the solid remelted and cast in chill molds. This procedure will give a sodium-lead alloy of high sodium (31.5%) content. Lower sodium content alloys of lead were easily prepared from this high sodium alloy by adding it in suitable amounts to molten lead.

3040 grams of copper were melted as in Example I and into this was stirred 1500 grams of zinc added in small portions. 30 grams of a 15% sodium-lead alloy were now added by holding beneath the surface of the melt. When the sodium fumes subsided the brass was cast.

This sodium-lead treated brass showed a dendritic structure with a tendency to polyhedric grains, whereas specimens not treated with sodium but containing an equivalent amount of lead showed a tendency to elongated dendrites.

The untreated and treated specimens were annealed at 5 50 C. for 30 minutes, cold worked to a reduction and then re-annealed at 550 C. for 30 minutes. The untreated specimens showed very irregular grain size with exaggerated grains running down the center, suggesting strains due to cold working. The sodium treated specimens showed an even grain size with no indication of an irregular grain size in the centers.

Similarly other sodium alloys of constituents of the final brass could be made and utilized for treating brasses. The quantity of sodium used'in the treating alloy is not fixed at any definite amount but may vary from very small amounts up to the maximum which will alloy with the particular constituent chosen. Thus the maximum which can be dissolved or alloyed with zinc is about 2% by weight. I! the amount of sodium necessary Ior proper treatment is greater than that which could be added by means of the zinc, which is of course improbable, a furtheramount of sodium can be added as an alloy of another constituent; thus also if the lead content or a lead brass is to be very low and sufficient sodium cannot be added by way of the sodium-lead alloy, the additional sodium required could be added by means of the zinc alloy. In Example I, sodium equivalent to 0.1% or the final weight of the brass was used and in general such amounts 'will be suflicient. Smaller quantities can be used and will be effective to the extent of the amount used. The exact amount to be utilized will depend on the nature of the composition and the qualities desired in the final brass. In some cases where there is an unusual amount of oxidized metal or impurities occluded in the molten brass it may be necessary to add considerably more sodium because 01' the reaction between such oxides or impurities and the sodium. It is .thought that the sodium in the brasses acts in part at least as a deoxidizer and degasifier but I am not certain of all of the reactions which may occur. Obviously, the above described zinc and copper proportions will produce one specific brass but other proportions within the whole range of brasses could be utilized.

I claim:

1. Method of treating brass with sodium which comprises adding said sodium thereto by means of a sodium-zinc alloy.

2. A method of treating brass with sodium which comprises adding said sodium thereto by means of a sodium-zinc alloy containing less than 2% by weight of sodium.

3. A method of treating brass with sodium which comprises adding said sodium thereto by means of a sodium-zinc alloy containing about 2% by weight of sodium.

WILLIAM F. ZIMMERLI. 

